V-set and Ig domain-containing 4 (VSIG-4 or VSIG4) is a C3 complement receptor, a B7 family-related protein, and a negative regulator of T cell activation. VSIG-4 expression has been observed to be restricted to tissue macrophages, and it has been shown to be down-regulated in response to lipopolysaccharide (LPS) (Vogt et al. (2006) J. of Clin. Invest. 116:2817). In healthy tissue, VSIG-4 is expressed on tissue-resident macrophages and functions as a complement receptor to opsonize bacterial pathogens. Massive infiltrates of VSIG-4+ macrophages into the tumor microenvironment have been observed in patients diagnosed with non-small cell lung cancer (Liao et al. (2014) Lab. Invest. 94:706), and high VSIG-4 expression has also been correlated with high-grade glioma and poor patient prognosis (Xu et al. (2015) Am. J. Transl. Res. 7:1172).